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Grehan, AJ;McKillen, M;Keegan, BF
Customisation of rapid visual reconnaissance technology for use within the deep sea - Sediment profile imagery.
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The utility of a rapid visual reconnaissance technique for benthic surveying of shallow soft bottom sediments has already been well demonstrated in the case of sediment profile imagery (SPI). This technique provides quantitative and qualitative data on the sediment water interface which can be used to make inferences about sediment health. Its rapidity in terms; of areal coverage and subsequent image analysis and reporting means that SPI has obvious advantages over traditional time consuming benthic survey techniques when rapid response to changes in environmental quality rue required.While SPI has mostly been used to provide rapid synoptic views of sediment health in shallow waters, its use in the deep-sea had received less attention. This paper describes the challenge of adapting sediment profile imagery for use down to abyssal depths as part of the EU funded MAST III project ALIPOR. Principal considerations were to counter the effects of pressure and cold, maximise sample number-deployment time ratio, facilitate ease of operation and allow ready access to generated images.Sediment profile imagery functions like an inverted periscope which, on penetrating the deposit, yields undisturbed images of the sediment/water interface. The device is built around a Kodak DCS 410 (1524 x 1012 pixel CCD array) with a Nikon N-90s camera. The basic SPI design is modified so that routine servicing and maintenance can be performed without removing the main pressure housing containing camera and batter ies. Two small pressure housing units sit on top of the main can. One of these contains the electronics and is easily removed if required. The second can has a removable lid and houses a SCSI port which provides the connection point for the attachment of a computer for image retrieval. Both lead-acid batteries and camera battery can be recharged without removal via a SeaConn connector linking the can interior to external intelligent battery chargers. The assembly has been successfully deployed to 4800m and is rated to 5500m. Once on the seafloor, up to 100 images can be taken by 'hopping' the,wire deployed system about the bottom using a frame attached acoustic pinger and wire tensionmeter to indicate when the machine is on the bottom.
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